The late, great US senator and sociologist Daniel Moynihan famously observed that everyone is entitled to their own opinion, but not to their own facts, and most of us nodded approvingly at the time. It neatly summed up our idealised notion of democratic discourse. So it’s entirely unsurprising that so many people are discombobulated to discover that apparently Moynihan’s maxim no longer applies. If nothing else, the Brexit vote and US presidential campaigns provided ample evidence of that. “Facts” became propositions that people felt ought to be true, even if they weren’t.

I’m a bit suspicious of the current despairing rhetoric about how we have moved into a “post-truth” society. First of all, it carries an implication that there was once a political golden age when “truth” really mattered. And secondly, it implies that establishing truth is a straightforward business – if only we could put our minds to it. Both of these propositions are, to put it politely, implausible.

Which brings us back to the problem of “fake news” – believed in some quarters to have had an impact on the US presidential election. Facebook has – rightly, because of its size and scope – been taking most of the heat from the resulting firestorm, but until recently seemed to regard the whole thing as a PR problem rather than something more fundamental. This is standard Silicon Valley operating procedure by the way: always try to deny responsibility in order to escape the tedious obligations that go with it. And of course for Facebook, there is the additional problem that its business model currently tends to favour fake news because – as a BuzzFeed analysis showed – it gets “shared” more and sharing is good for the bottom line. Or, as Frederic Filloux put it with brutal clarity: “Facebook’s walled wonderland is inherently incompatible with news”.

Watching the Facebook boss squirming on the fake-news hook provides a sharp vignette of the Silicon Valley elite: stratospheric IQ combined with childlike naivety. Now that it has dawned on him that this might be a really serious problem – especially under a president who isn’t overawed by the aura of tech companies – there are doubtless lots of project teams working frantically within Facebook to find a solution to the fake-news problem. This week we’ve seen interesting evidence of one approach they are trying – surveying their users to see how good they are at spotting spoof stories.

According to the Verge tech news website, in one case they are shown a tweet from the Philadelphia Inquirer boosting a story about the local baseball team sacking a peanut vendor known as “Pistachio Girl” for her involvement in “white identity politics”. The headline on the tweet reads “Pistachio Girl has been fired from her Citizens Bank Park job”. (Citizens Bank Park is the team’s stadium.) The survey question was “To what extent do you think this link’s title uses misleading language?” on a five-point scale from “not at all” to “completely”. Another user was shown a different link and posed a different question: “To what extent do you think this link’s title withholds key details of the story?”

If Facebook thinks it can outsource the detection of fake news to its users (and thereby avoid accepting editorial responsibility) then Stanford University has some bad news for it. Over the past 18 months the university’s history education group has been testing the ability of 7,800 “digital natives” (ie at middle school, high school and college students) in 12 states to judge the credibility of online information.

The results, in the words of the researchers, are “dismaying”, “bleak” and “a threat to democracy”. The students were duped again and again. They couldn’t tell fake accounts from real ones, activist groups from neutral sources or distinguish ads from articles. More than 80% of middle-school (11- to 13-year-old) children thought that “sponsored content” was a real news story. They were suckers for professionally produced and attractive web pages, and a fluent and polished “about” page was enough to persuade many that the site was authoritative.

And when asked to evaluate the trustworthiness of information on two websites, one published by the 66,000-member American Academy of Pediatrics, established in 1930 and publisher of the journal Pediatrics, the other by the American College of Pediatricians, a conservative fringe group that broke with the main organisation in 2002 over its stance on adoption by same-sex couples, more than half of the Stanford undergraduates in the study concluded that the second group was “more reliable”. So: back to the drawing board, Mr Zuckerberg.